U.S. patent number 6,891,589 [Application Number 10/733,445] was granted by the patent office on 2005-05-10 for optical film, elliptically polarizing plate and image display.
This patent grant is currently assigned to Nitto Denko Corporation. Invention is credited to Masahiro Hata, Hiroyuki Okada, Kiichi Shimodaira.
United States Patent |
6,891,589 |
Hata , et al. |
May 10, 2005 |
Optical film, elliptically polarizing plate and image display
Abstract
A laminated optical film including an optical film (1) whose
three dimensional refractive index is controlled so that an Nz
coefficient represented with Nz=(nx.sub.1 -nz.sub.1)/(nx.sub.1
-ny.sub.1) satisfies a relationship of Nz.ltoreq.0.9, when a
direction where a refractive index in a film plane gives maximum is
defined as X-axis, a direction perpendicular to X-axis as Y-axis, a
thickness direction of the film as Z-axis, and refractive indexes
in each axial direction are defined as nx.sub.1, ny.sub.1, and
nz.sub.1, respectively, and an optical film (2) that is formed with
a material showing optically negative uniaxial property, and being
tilting aligned. The laminated optical film may suppress coloring
of the display, and may display a picture with few tone reversal
regions.
Inventors: |
Hata; Masahiro (Ibaraki,
JP), Okada; Hiroyuki (Ibaraki, JP),
Shimodaira; Kiichi (Ibaraki, JP) |
Assignee: |
Nitto Denko Corporation
(Ibaraki, JP)
|
Family
ID: |
32396322 |
Appl.
No.: |
10/733,445 |
Filed: |
December 12, 2003 |
Foreign Application Priority Data
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|
|
|
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Dec 16, 2002 [JP] |
|
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2002-363696 |
Jan 18, 2003 [JP] |
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2003-001791 |
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Current U.S.
Class: |
349/117; 349/118;
349/119 |
Current CPC
Class: |
G02B
5/3083 (20130101); G02B 5/3033 (20130101); G02B
5/3016 (20130101); G02F 1/13363 (20130101) |
Current International
Class: |
G02B
5/30 (20060101); G02F 1/13 (20060101); G02F
001/13 () |
Field of
Search: |
;349/117-121 |
References Cited
[Referenced By]
U.S. Patent Documents
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|
|
5406396 |
April 1995 |
Akatsuka et al. |
5587821 |
December 1996 |
Nakanishi et al. |
5825445 |
October 1998 |
Okamoto et al. |
5859681 |
January 1999 |
VanderPloeg et al. |
5895106 |
April 1999 |
VanderPloeg et al. |
5923392 |
July 1999 |
Akatsuka et al. |
5986732 |
November 1999 |
Ozeki et al. |
6292242 |
September 2001 |
VanderPloeg et al. |
6330108 |
December 2001 |
Nishikouji et al. |
6433853 |
August 2002 |
Kameyama et al. |
6480251 |
November 2002 |
Yamaguchi et al. |
6667835 |
December 2003 |
Yano et al. |
6762811 |
July 2004 |
Sasaki et al. |
6771340 |
August 2004 |
Yoshimi et al. |
|
Foreign Patent Documents
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|
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0 482 620 |
|
Apr 1992 |
|
EP |
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0 962 805 |
|
Dec 1999 |
|
EP |
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1 069 461 |
|
Jan 2001 |
|
EP |
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1 087 254 |
|
Mar 2001 |
|
EP |
|
5-100114 |
|
Apr 1993 |
|
JP |
|
10-68816 |
|
Mar 1998 |
|
JP |
|
10-90521 |
|
Apr 1998 |
|
JP |
|
Primary Examiner: Dudek; James A.
Attorney, Agent or Firm: Westerman, Hattori Daniels &
Adrian LLP
Claims
What is claimed is:
1. A laminated optical film comprising: an optical film (1) whose
three dimensional refractive index is controlled so that an Nz
coefficient represented with Nz=(nx.sub.1 -nz.sub.1)/(nx.sub.1
-ny.sub.1) satisfies a relationship of Nz.ltoreq.0.9, when a
direction where a refractive index in a film plane gives maximum is
defined as X-axis, a direction perpendicular to X-axis as Y-axis, a
thickness direction of the film as Z-axis, and refractive indexes
in each axial direction are defined as nx.sub.1, ny.sub.1, and
nz.sub.1, respectively, an optical film (2) that is formed with a
material showing optically negative uniaxial property, and being
tilting aligned, and an optical film (3) that satisfies nx.sub.3
>ny.sub.3.apprxeq.nz.sub.3 and demonstrates optically positive
uniaxial property, when a direction where a refractive index in a
film plane gives maximum is defined as X-axis, a direction
perpendicular to X-axis as Y-axis, a thickness direction of the
film as Z-axis, and refractive indexes in each axial direction are
defined as nx.sub.3, ny.sub.3, and nz.sub.3, respectively.
2. The laminated optical film according to claim 1, wherein the Nz
coefficient of the optical film (1) having the controlled three
dimensional refractive index satisfies a relationship of
Nz.ltoreq.0.3.
3. The laminated optical film according to claim 1, wherein the
material showing optically negative uniaxial property forming the
optical film (2) is a discotic liquid crystal compound.
4. The laminated optical film according to claim 1, wherein the
material showing optically negative uniaxial property forming the
optical film (2) is tilting aligned so that an average optical
axis, and a direction of normal line of the optical film (2) give a
tilting angle in a range of 5 degrees to 50 degrees.
5. The laminated optical film according to claim 1, wherein the
optical film (1) having the controlled three dimensional refractive
index is arranged between the optical film (3) showing optically
positive uniaxial property and the optical film (2) in which a
material showing optically negative uniaxial property is tilting
aligned.
6. An elliptically polarizing plate comprising: the laminated
optical film according to claim 1 and a polarizing plate.
7. The elliptically polarizing plate according to claim 6, wherein
the polarizing plate is laminated on a side of the optical film (3)
of the laminated optical film.
8. An image display comprising the laminated optical film according
to claim 1.
9. An image display comprising the elliptically polarizing plate
according to claim 6.
10. The image display of claim 9, wherein the laminated optical
film is disposed on one side of a liquid crystal cell.
11. The image display of claim 10, wherein the laminated optical
film is mounted on a backlight side of the liquid crystal cell.
12. The laminated optical film according to claim 5, wherein the Nz
coefficient of the optical film (1) having the controlled three
dimensional refractive index satisfies a relationship of
Nz.ltoreq.0.3.
13. The laminated optical film according to claim 5, wherein the
material showing optically negative uniaxial property forming the
optical film (2) is a discotic liquid crystal compound.
14. The laminated optical film according to claim 5, wherein the
material showing optically negative uniaxial property forming the
optical film (2) is tilting aligned so that an average optical
axis, and a direction of normal line of the optical film (2) give a
tilting angle in a range of 5 degrees to 50 degrees.
15. An elliptically polarizing plate comprising: the laminated
optical film according to claim 5 and a polarizing plate.
16. The elliptically polarizing plate according to claim 15,
wherein the polarizing plate is laminated on a side of the optical
film (3) of the laminated optical film.
17. An image display comprising the laminated optical film
according to claim 5.
18. An image display comprising the elliptically polarizing plate
according to claim 15.
19. The image display of claim 18, wherein the laminated optical
film is disposed on one side of a liquid crystal cell.
20. The image display of claim 19, wherein the laminated optical
film is mounted on a backlight side of the liquid crystal cell.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a laminated optical film. A
laminated optical film of this invention may be used as various
optical films such as a retardation plate, a viewing angle
compensating film, an optical compensating film, an elliptically
polarizing plate (including a circularly polarizing plate), and a
brightness enhancement film, independently or in combination with
other optical films. Especially in the case where it is used as an
elliptically polarizing plate laminated with a polarizing plate, a
laminated optical film of this invention is useful. Moreover, this
invention relates to an image display, such as a liquid crystal
display, an organic EL (electroluminescence) display, a PDP, etc.
using the laminated optical film, and elliptically polarizing
plate, etc. The laminated optical film and the elliptically
polarizing plate of this invention may be used to various liquid
crystal displays etc. as mentioned above, and may be utilized
particularly suitably for a reflective semi-transmission type
liquid crystal display that can be mounted in portable information
and telecommunications instruments, and personal computer, etc.
Prior Art
Conventionally, a broadband retardation plate that functions as a
quarter wavelength plate or a half wavelength plate to incident
light (in visible light region) having a wavelength in broadband
has been suitably used in reflective semi-transmission type liquid
crystal displays etc. As such broadband retardation plates, a
laminated film is proposed in which a plurality of polymer films
having optical anisotropy are laminated with optical axes being
made to mutually intersect. Broadband is realized in these
laminated films by intersection of optical axes of two sheets or a
plurality of sheets of stretched films. For example, refer to
Japanese Patent Laid-Open No.5-100114 official gazette, Japanese
Patent Laid-Open No.10-68816 official gazette, and Japanese Patent
Laid-Open No.10-90521 official gazette.
However, there have been defects that observation of an display in
vertically and horizontally diagonal directions with respect to a
direction of normal line of a screen causes tone reversal that
gives a varied hue of the display or a reversal between white
pictures and black pictures, even when a broadband retardation
plate having a constitution disclosed in the above-mentioned
Referential Patents is used.
SUMMARY OF THE INVENTION
The present invention aims at providing an optical film in which
observation of a display in a diagonal direction with respect to a
direction of a normal line of a picture may suppress coloring of
the display, and, as a result, may display a picture with few tone
reversal regions.
Besides, the present invention aims at providing an elliptically
polarizing plate in which the above-mentioned optical film and
polarizing plate are laminated. Furthermore, this invention aims at
providing an image display using the above-mentioned optical film
or the elliptically polarizing plate.
Wholehearted research performed by the present inventors in order
to solve the above-mentioned subject revealed that use of following
laminated optical films might attain the above-described object,
and resulted in completion of the present invention.
That is, the present invention relates to a laminated optical film
comprising an optical film (1) whose three dimensional refractive
index is controlled so that an Nz coefficient represented with
Nz=(nx.sub.1 -nz.sub.1)/(nx.sub.1 -ny.sub.1) satisfies a
relationship of Nz.ltoreq.0.9, when a direction where a refractive
index in a film plane gives maximum is defined as X-axis, a
direction perpendicular to X-axis as Y-axis, a thickness direction
of the film as Z-axis, refractive indexes in each axial direction
are defined as nx.sub.1, ny.sub.1, and nz.sub.1, respectively,
and an optical film (2) that is formed with a material showing
optically negative uniaxial property, and being tilting
aligned.
In a laminated optical film of the present invention described
above, an optical film (1) having a controlled three dimensional
refractive index, and an optical film (2) in which a material
showing optically negative uniaxial property is tilting aligned are
laminated, which is useful as a retardation plate having
compensating property over a broadband and wide viewing angle.
Image displays such as liquid crystal displays using the laminated
optical film concerned may realize a wide viewing angle, and
moreover, observation in diagonal directions with respect to a
display screen suppresses display coloring, and therefore may
display a picture having few tone reversal regions.
In the optical film (1) whose three dimensional refractive index is
controlled, an Nz coefficient defined by the above-mentioned
description is Nz.ltoreq.0.9. The Nz coefficient of Nz>0.9 may
not easily realize a wide viewing angle, and may not sufficiently
suppress display coloring in case of observation in diagonal
directions of a display screen, but provides reversal of contrast,
that is, tone reversal in diagonal directions. The smaller Nz
coefficient the better, and preferably it satisfies Nz.ltoreq.0.3,
and more preferably Nz.ltoreq.0.2. In addition, in the optical film
(1), a case of (nx.sub.1 -nz.sub.1)<0 may be included and the Nz
coefficient may have negative values. However, in view of a viewing
angle expansion in vertical and horizontal direction, the Nz
coefficient is preferably controlled -1 or more, and more
preferably -0.5 or more.
In the above-mentioned laminated optical film, the material showing
optically negative uniaxial property forming the optical film (2),
it is preferably of a discotic liquid crystal compound. Although a
material showing optically negative uniaxial property is not
especially limited, but a discotic liquid crystal compound is
preferable in view of realization of effective control of tilted
alignment, commonly available material, and comparatively low
cost.
In the above-mentioned laminated optical film, the material showing
optically negative uniaxial property forming the optical film (2)
is preferably tilting aligned so that an average optical axis, and
a direction of normal line of the optical film (2) may give a
tilting angle in a range of 5 degrees to 50 degrees.
The optical film (2) is combined with the optical film (1) having a
controlled three-dimensional refractive index to be used as the
laminated optical film as mentioned above. And when it is mounted
in liquid crystal displays etc., it may demonstrate a large viewing
angle expansion effect by controlling the above-mentioned tilting
angle of the optical film (2) to be at 5 degrees or more. On the
other hand, excellent viewing angle is realized in any directions
in vertical and horizontal directions (four directions) by
controlling the above-mentioned tilting angle at 50 degrees or
less, and therefore a phenomenon may be suppressed in which quality
of a viewing angle is variable dependent on directions. In the
viewpoint of the above-mentioned reason, the tilting angle is
preferably in a range of 10 degrees to 30 degrees.
Besides, a state of tilted alignment of optical material (for
example, discotic liquid crystalline molecule) showing optically
negative uniaxial property may be a uniform tilted alignment that
does not vary in connection with a distance from an inside of a
film plane, and may vary in connection with a distance between the
above-mentioned optical material and inside of the film plane.
Furthermore, the present invention relates to a laminated optical
film comprising: the above-mentioned laminated optical film and an
optical film (3) that satisfies nx.sub.3
>ny.sub.3.apprxeq.nz.sub.3 and demonstrates optically positive
uniaxial property when a direction where a refractive index in a
film plane gives maximum is defined as X-axis, a direction
perpendicular to X-axis as Y-axis, a thickness direction of the
film as Z-axis, and refractive indexes in each axial direction are
defined as nx.sub.3, ny.sub.3, and nz.sub.3, respectively.
The optical film (3) showing optically positive uniaxial property
is further laminated to the laminated optical film in which the
optical film (1) having a controlled three dimensional refractive
index and the optical film (2) in which a material showing
optically negative uniaxial property is tilting aligned are
laminated. And thereby image displays such as liquid crystal
displays, using the laminated optical film concerned, may realize a
more wide viewing angle, suppress display coloring in case of
observation in diagonal directions with respect go a display
screen, and moreover may display pictures having few tone reversal
regions.
In the above-mentioned laminated optical film in which the optical
film (3) is laminated, a constitution, in which the optical film
(1) having the controlled three dimensional refractive index is
arranged between the optical film (3) showing optically positive
uniaxial property, and the optical film (2) in which the material
showing optically negative uniaxial property is tilting aligned,
may realize a wide viewing angle, which is preferable in order to
control more effectively a tone reversal region in case of
observation in diagonal directions.
Moreover, the present invention relates to an elliptically
polarizing plate in which the above-mentioned laminated optical
film and a polarizing plate are laminated. The above-mentioned
elliptically polarizing plate is a laminated optical film in which
the optical film (3) is laminated, a constitution in which a
polarizing plate is laminated on a side of the optical film (3) is
preferable in view of tone reversal region in case of observation
in diagonal directions.
Furthermore, the present invention relates to an image display in
which the above-mentioned laminated optical film or elliptically
polarizing plate is laminated.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows one embodiment of a sectional view of a laminated
optical film of the present invention;
FIG. 2 shows one embodiment of a sectional view of a laminated
optical film of the present invention;
FIG. 3 shows one embodiment of a sectional view of a laminated
optical film of the present invention;
FIG. 4 shows one embodiment of a sectional view of a laminated
optical film of the present invention;
FIG. 5 shows one embodiment of a sectional view of an elliptically
polarizing plate of the present invention;
FIG. 6 shows one embodiment of a sectional view of an elliptically
polarizing plate of the present invention;
FIG. 7 shows one embodiment of a sectional view of an elliptically
polarizing plate of the present invention;
FIG. 8 shows one embodiment of a sectional view of an elliptically
polarizing plate of Referential Example; and
FIG. 9 shows a sectional view of an example of a reflective
semi-transmission type liquid crystal display of Example.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A laminated optical film of the present invention, hereinafter, is
described referring to drawings. As shown in FIG. 1, in a laminated
optical film of the present invention, an optical film (1) having a
controlled three dimensional refractive index, and an optical film
(2) in which a material showing optically negative uniaxial
property is tilting aligned are laminated. FIG. 2 or 4 show a
laminated optical film in which an optical film (3) showing
optically positive uniaxial property is further laminated to the
above-mentioned optical film. In FIG. 2, the optical film (3) is
laminated on a side of the optical film (1), and in FIG. 3, the
optical film (3) is laminated on a side of the optical film (2). In
addition, in FIG. 4, the optical film (3) is laminated between the
optical film (1) and the optical film (2). Lamination position of
the optical film (3) may be on a side of the optical film (2)
and/or on a side of the optical film (1), and, furthermore, may be
any position between them. As FIG. 2 shows, the optical film (3) is
preferably arranged on a side of the optical film (1), and the
optical film (1) is laminated between the optical film (2) and the
optical films (3).
Besides, a polarizing plate (P) may be laminated to the laminated
optical film to obtain an elliptically polarizing plate. FIGS. 5 to
7 show an elliptically polarizing plate (P1) in which a polarizing
plate (P) is laminated to the laminated optical film shown in FIGS.
2 to 4. In addition, a lamination position of the polarizing plate
(P) with respect to the laminated optical film is not especially
limited, and since it extends a viewing angle wider when mounted in
liquid crystal display, the polarizing plate (P) is preferably
laminated on a side of the optical film (3) as shown in FIGS. 5 to
6. Particularly a case of FIG. 5 is preferable.
Furthermore, in FIG. 1 to FIG. 7, each optical film and polarizing
plate are laminated via pressure sensitive adhesive layers (a). The
pressure sensitive adhesive layer (a) may be single-layered, and
may be multi-layered with plurality of layers.
As an optical film (1) having a controlled three dimensional
refractive index, any optical film may be used as long as an Nz
coefficient thereof represented with Nz=(nx.sub.1
-nz.sub.1)/(nx.sub.1 -ny.sub.1) satisfies a relationship of
Nz.ltoreq.0.9, when a direction where a refractive index in a film
plane gives maximum is defined as X-axis, a direction perpendicular
to X-axis as Y-axis, a thickness direction of the film as Z-axis,
refractive indexes in each axial direction are defined as nx.sub.1,
ny.sub.1, and nz.sub.1, respectively.
Methods for manufacturing an optical film (1) is not especially
limited, and there may be mentioned: for example, a method in which
a polymer film is stretched biaxially in a direction of a plane,
and a method in which a polymer film is uniaxially or biaxially
stretched in a direction of a plane, and then is stretched also in
a thickness direction. Furthermore, a method in which a thermal
shrinkable film is adhered to a polymer film, and stretching
processing and/or shrinking process are given to the polymer film
under influence of shrinking force caused by heating may be
mentioned. A refractive index in a thickness direction is
controlled by these methods, and alignment state is controlled so
that a three dimensional refractive index of the resulting
stretched film may be Nz.ltoreq.0.9.
As polymers for forming the optical film (1), for example,
polycarbonates; polyolefins such as polypropylenes; polyesters such
as polyethylene terephthalates and polyethylenenaphthalates;
norbornene polymers; polyvinyl alcohols; polyvinyl butyrals;
polymethyl vinyl ethers; polyhydroxyethyl acrylates; hydroxyethyl
celluloses; hydroxy propylcelluloses; methylcelluloses;
polyallylates; polysulfones; polyethersulfones; polyphenylene
sulfides; polyphenylene oxides; polyallyl sulfones; polyamides;
polyimides; polyvinyl chlorides; cellulose polymers such as
triacetyl celluloses, etc.; acrylic polymers; styrene polymers or
binary based or ternary based various copolymers, graft copolymers,
blended materials thereof may be mentioned.
In the optical film (1), Nz.ltoreq.0.9, but a front retardation
thereof ((nx.sub.1 -ny.sub.1).times.d.sub.1 (thickness: nm)) is
preferably 10 to 400 nm, and more preferably 50 to 200 nm. A
retardation in a thickness direction ((nx.sub.1
-nz.sub.1).times.d.sub.1) is preferably 10 to 400 nm, and more
preferably 50 to 300 nm.
A thickness (d.sub.1) of the optical film (1) is not especially
limited, but preferably it is 1 to 150 micrometers, and more
preferably 5 to 50 micrometers.
The material showing optically negative uniaxial property forming
the optical film (2) represents a material in which a refractive
index of principal axis in one direction is smaller than refractive
indexes in other two directions for an ellipsoid having three
dimensional refractive index.
As materials showing optically negative uniaxial property,
polyimide based materials, and liquid crystal based materials such
as discotic liquid crystal compounds may be mentioned. Moreover,
there may be mentioned materials in which these materials as a
principal component are mixed and reacted with the other oligomers
and polymers to obtain a fixed state in a film form of tilted
alignment of the material showing negative uniaxial property. When
discotic liquid crystal compounds are used, an tilted alignment
state of liquid crystalline molecules may be controlled by a
molecular structure, by a kind of alignment layer, and by use of
additives (for example, plasticizers, binders, surface active
agents) being added appropriately into an optical anisotropic
layer.
A front retardation ((nx.sub.2 -ny.sub.2).times.d.sub.2 (thickness:
nm)) of the optical film (2) is preferably 0 to 200 nm, and more
preferably 1 to 150 nm, when a direction where a refractive index
in a film plane of the optical film (2) gives maximum is defined as
X-axis, a direction perpendicular to X-axis as Y-axis, a thickness
direction of the film as Z-axis, refractive indexes in each axial
direction are defined as nx.sub.2, ny.sub.2, and nz.sub.2,
respectively. A retardation in a thickness direction ((nx.sub.2
-nz.sub.2).times.d.sub.2) is preferably 10 to 400 nm, and more
preferably 50 to 300 nm.
A thickness (d.sub.2) of the optical film (2) is not especially
limited, but it is preferably 1 to 200 micrometers, and more
preferably 2 to 150 micrometers.
In conducting lamination for the optical film (1) and the optical
film (2), the films are preferably laminated so that an each slow
axis of the films may give an angle, which is smaller than other
angle, in a range of 70 degrees to 90 degrees, more preferably in a
range of 80 degrees to 90 degrees.
As optical films (3) showing optically positive uniaxial property,
materials satisfying a relationship of nx.sub.3
>ny.sub.3.apprxeq.nz.sub.3 may be used without particular
limitation, where a direction in which a refractive index in a film
plane gives maximum is defined as X-axis, a direction perpendicular
to X-axis as Y-axis, a thickness direction of the film as Z-axis,
refractive indexes in each axial direction are defined as nx.sub.3,
ny.sub.3, and nz.sub.3, respectively. That is, a material showing
optically positive uniaxial property represents a material in which
a refractive index of principal axis in one direction is larger
than refractive indexes in other two directions for an ellipsoid
having three-dimensional refractive index.
The optical film (3) showing optically positive uniaxial property
(3) may be obtained, for example, by giving a uniaxial stretching
process in a planar direction to a polymer film illustrated in the
optical film (1). Besides, rodlike nematic liquid crystalline
compounds may also be used. Rodlike nematic liquid crystalline
compounds may be tilting aligned, whose tilted alignment state may
be controlled by a molecular structure, by a kind of alignment
layer, and by use of additives (for example, plasticizers, binders,
surface active agents) added appropriately into an optical
anisotropic layer.
A front retardation ((nx.sub.3 -ny.sub.3).times.d.sub.3 (thickness:
nm)) of the optical film (3) is preferably 0 to 500 nm, and more
preferably 1 to 350 nm. A retardation in a thickness direction
((nx.sub.3 -nz.sub.3).times.d.sub.3) is preferably 0 to 500 nm, and
more preferably 1 to 350 nm.
A thickness (d.sub.3) of the optical film (3) is not especially
limited, but preferably it is 1 to 200 micrometers, and more
preferably 2 to 80 micrometers.
A polarizing plate (P) may be usually used a polarizer with a
transparent protective film prepared on one side or both sides of
the polarizer. The polarizer is not limited especially but various
kinds of polarizer may be used. As a polarizer, for example, a film
that is uniaxially stretched after having dichromatic substances,
such as iodine and dichromatic dye, absorbed to hydrophilic high
molecular weight polymer films, such as polyvinyl alcohol type
film, partially formalized polyvinyl alcohol type film, and
ethylene-vinyl acetate copolymer type partially saponified film;
poly-ene type orientation films, such as dehydrated polyvinyl
alcohol and dehydrochlorinated polyvinyl chloride, etc. may be
mentioned. In these, a polyvinyl alcohol type film on which
dichromatic materials (iodine, dyes) is absorbed and oriented after
stretched is suitably used. Although thickness of polarizer is not
especially limited, the thickness of about 5 to 80 .mu.m is
commonly adopted.
A polarizer that is uniaxially stretched after a polyvinyl alcohol
type film dyed with iodine is obtained by stretching a polyvinyl
alcohol film by 3 to 7 times the original length, after dipped and
dyed in aqueous solution of iodine. If needed the film may also be
dipped in aqueous solutions, such as boric acid and potassium
iodide, which may include zinc sulfate, zinc chloride.
Furthermore, before dyeing, the polyvinyl alcohol type film may be
dipped in water and rinsed if needed. By rinsing polyvinyl alcohol
type film with water, effect of preventing un-uniformity, such as
unevenness of dyeing, is expected by making polyvinyl alcohol type
film swelled in addition that also soils and blocking inhibitors on
the polyvinyl alcohol type film surface may be washed off.
Stretching may be applied after dyed with iodine or may be applied
concurrently, or conversely dyeing with iodine may be applied after
stretching. Stretching is applicable in aqueous solutions, such as
boric acid and potassium iodide, and in water bath.
As the transparent protective film prepared on one side or both
sides of the polarizer, materials is excellent in transparency,
mechanical strength, heat stability, water shielding property,
isotropy, etc. may be preferably used. As materials of the
above-mentioned protective layer, for example, polyester type
polymers, such as polyethylene terephthalate and
polyethylenenaphthalate; cellulose type polymers, such as diacetyl
cellulose and triacetyl cellulose; acrylics type polymer, such as
polymethylmethacrylate; styrene type polymers, such as polystyrene
and acrylonitrile-styrene copolymer (AS resin); polycarbonate type
polymer may be mentioned. Besides, as examples of the polymer
forming a protective film, polyolefin type polymers, such as
polyethylene, polypropylene, polyolefin that has cyclo-type or
norbornene structure, ethylene-propylene copolymer; vinyl chloride
type polymer; amide type polymers, such as nylon and aromatic
polyamide; imide type polymers; sulfone type polymers; polyether
sulfone type polymers; polyether-etherketone type polymers;
polyphenylene sulfide type polymers; vinyl alcohol type polymer;
vinylidene chloride type polymers; vinyl butyral type polymers;
allylate type polymers; polyoxymethylene type polymers; epoxy type
polymers; or blend polymers of the above-mentioned polymers may be
mentioned. Films made of heat curing type or ultraviolet ray curing
type resins, such as acryl based, urethane based, acryl urethane
based, epoxy based, and silicone based, etc. may be mentioned.
Moreover, as is described in Japanese Patent Laid-Open Publication
No. 2001-343529 (WO 01/37007), polymer films, for example, resin
compositions including (A) thermoplastic resins having substituted
and/or non-substituted imido group is in side chain, and (B)
thermoplastic resins having substituted and/or non-substituted
phenyl and nitrile group in sidechain may be mentioned. As an
illustrative example, a film may be mentioned that is made of a
resin composition including alternating copolymer comprising
iso-butylene and N-methyl maleimide, and acrylonitrile-styrene
copolymer. A film comprising mixture extruded article of resin
compositions etc. may be used.
As a transparent protective film preferably used, in viewpoint of
polarization property and durability, triacetyl cellulose film
whose surface is saponificated with alkali is suitable. In general,
a thickness of a transparent protective film is about 10 through
500 .mu.m, preferably 20 through 300 .mu.m, and especially
preferably 30 through 200 .mu.m.
Moreover, it is preferable that the transparent protective film may
have as little coloring as possible. Accordingly, a protective film
having a phase difference value in a film thickness direction
represented by Rth=[(nx+ny)/2-nz].times.d of -90 nm through +75 nm
(where, nx and ny represent principal indices of refraction in a
film plane, nz represents refractive index in a film thickness
direction, and d represents a film thickness) may be preferably
used. Thus, coloring (optical coloring) of polarizing plate
resulting from a protective film may mostly be cancelled using a
protective film having a phase difference value (Rth) of -90 nm
through +75 nm in a thickness direction. The phase difference value
(Rth) in a thickness direction is preferably -80 nm through +60 nm,
and especially preferably -70 nm through +45 nm.
As a transparent protective film, if polarization property and
durability are taken into consideration, cellulose based polymer,
such as triacetyl cellulose, is preferable, and especially
triacetyl cellulose film is suitable. In addition, when transparent
protective films are provided on both sides of the polarizer,
transparent protective films comprising same polymer material may
be used on both of a front side and a back side, and transparent
protective films comprising different polymer materials etc. may be
used. Adhesives are used for adhesion processing of the above
described polarizer and the transparent protective film. As
adhesives, polyvinyl alcohol derived adhesives, gelatin derived
adhesives, vinyl polymers derived latex type, aqueous polyurethane
based adhesives, aqueous polyesters derived adhesives, etc. may be
mentioned.
A hard coat layer may be prepared, or antireflection processing,
processing aiming at sticking prevention, diffusion or anti glare
may be performed onto the face on which the polarizing film of the
above described transparent protective film has not been adhered. A
hard coat processing is applied for the purpose of protecting the
surface of the polarizing plate from damage, and this hard coat
film may be formed by a method in which, for example, a curable
coated film with excellent hardness, slide property etc. is added
on the surface of the protective film using suitable ultraviolet
curable type resins, such as acrylic type and silicone type resins.
Antireflection processing is applied for the purpose of
antireflection of outdoor daylight on the surface of a polarizing
plate and it may be prepared by forming an antireflection film
according to the conventional method etc. Besides, a sticking
prevention processing is applied for the purpose of adherence
prevention with adjoining layer.
In addition, an anti glare processing is applied in order to
prevent a disadvantage that outdoor daylight reflects on the
surface of a polarizing plate to disturb visual recognition of
transmitting light through the polarizing plate, and the processing
may be applied, for example, by giving a fine concavo-convex
structure to a surface of the protective film using, for example, a
suitable method, such as rough surfacing treatment method by
sandblasting or embossing and a method of combining transparent
fine particle. As a fine particle combined in order to form a fine
concavo-convex structure on the above-mentioned surface,
transparent fine particles whose average particle size is 0.5 to 50
.mu.m, for example, such as inorganic type fine particles that may
have conductivity comprising silica, alumina, titania, zirconia,
tin oxides, indium oxides, cadmium oxides, antimony oxides, etc.,
and organic type fine particles comprising cross-linked of
non-cross-linked polymers may be used. When forming fine
concavo-convex structure on the surface, the amount of fine
particle used is usually about 2 to 50 weight part to the
transparent resin 100 weight part that forms the fine
concavo-convex structure on the surface, and preferably 5 to 25
weight part. An anti glare layer may serve as a diffusion layer
(viewing angle expanding function etc.) for diffusing transmitting
light through the polarizing plate and expanding a viewing angle
etc.
In addition, the above-mentioned antireflection layer, sticking
prevention layer, diffusion layer, anti glare layer, etc. may be
built in the protective film itself, and also they may be prepared
as an optical layer different from the protective layer.
As pressure sensitive adhesive that forms adhesive layer(a) is not
especially limited, and, for example, acrylic type polymers;
silicone type polymers; polyesters, polyurethanes, polyamides,
polyethers; fluorine type and rubber type polymers may be suitably
selected as a base polymer. Especially, a pressure sensitive
adhesive such as acrylics type pressure sensitive adhesives may be
preferably used, which is excellent in optical transparency,
showing adhesion characteristics with moderate wettability,
cohesiveness and adhesive property and has outstanding weather
resistance, heat resistance, etc.
Proper method may be carried out to attach an adhesive layer to one
side or both sides of the optical film. As an example, about 10 to
40 weight % of the pressure sensitive adhesive solution in which a
base polymer or its composition is dissolved or dispersed, for
example, toluene or ethyl acetate or a mixed solvent of these two
solvents is prepared. A method in which this solution is directly
applied on a polarizing plate top or an optical film top using
suitable developing methods, such as flow method and coating
method, or a method in which an adhesive layer is once formed on a
separator, as mentioned above, and is then transferred on a
polarizing plate or an optical film may be mentioned.
The adhesive layer may contain additives, for example, such as
natural or synthetic resins, adhesive resins, glass fibers, glass
beads, metal powder, fillers comprising other inorganic powder
etc., pigments, colorants and antioxidants. Moreover, it may be an
adhesive layer that contains fine particle and shows optical
diffusion nature.
Thickness of an adhesive layer may be suitably determined depending
on a purpose of usage or adhesive strength, etc., and generally is
1 to 500 .mu.m, preferably 5 to 200 .mu.m, and more preferably 10
to 100 .mu.m.
A temporary separator is attached to an exposed side of an adhesive
layer to prevent contamination etc., until it is practically used.
Thereby, it can be prevented that foreign matter contacts adhesive
layer in usual handling. As a separator, without taking the
above-mentioned thickness conditions into consideration, for
example, suitable conventional sheet materials that is coated, if
necessary, with release agents, such as silicone type, long chain
alkyl type, fluorine type release agents, and molybdenum sulfide
may be used. As a suitable sheet material, plastics films, rubber
sheets, papers, cloths, no woven fabrics, nets, foamed sheets and
metallic foils or laminated sheets thereof may be used.
In addition, in the present invention, ultraviolet absorbing
property may be given to the above-mentioned each layer, such as a
polarizer for a polarizing plate, a transparent protective film and
an optical film etc. and an adhesive layer, using a method of
adding UV absorbents, such as salicylic acid ester type compounds,
benzophenol type compounds, benzotriazol type compounds, cyano
acrylate type compounds, and nickel complex salt type
compounds.
The elliptically polarizing plate of the present invention may
suitably be used in image displays. For example, it may be
preferably used for formation of various apparatus, such as liquid
crystal displays of reflective semi-transmission type. Reflective
semi-transmission type liquid crystal displays etc. may be suitably
used as portable information and telecommunications instruments and
personal computers. When forming a reflected type semi-transmission
type liquid crystal display, an elliptically polarizing plate of
this invention is arranged on a backlight (BL) of a liquid crystal
cell.
In FIG. 9, an elliptically polarizing plate (P1) of the present
invention shown in FIG. 5 or 7 is arranged via a pressure sensitive
adhesive layer, on a side of a backlight (BL) of a liquid crystal
cell (L) in a reflective semi-transmission type liquid crystal
display. Although an arranged side of an elliptically polarizing
plate (P1) being laminated on a lower side (backlight side) of
liquid crystal cell (L) is not especially limited, it is preferably
arranged so that a polarizing plate (P) of the elliptically
polarizing plate (P1) may be most separated from the liquid crystal
cell (L) side. Liquid crystal is enclosed within a liquid crystal
cell (L). A transparent electrode is provided on an upper liquid
crystal cell substrate, and a reflecting layer serving also as an
electrode is provided on a lower liquid crystal cell substrate. An
elliptically polarizing plate (P2) and various optical films that
are used for reflective semi-transmission type liquid crystal
displays are arranged on an upper side of liquid crystal cell
substrate. The elliptically polarizing plate (P2) may also
preferably arrange so that the polarizing plate (P) may be most
separated from the liquid crystal cell (L) side.
Besides, when the laminated optical film and the elliptically
polarizing plate of the present invention are mounted in a liquid
crystal display etc., in the optical film (2), an average optical
axis (an average angle of tilted alignment) of a material showing
optically negative uniaxial property is preferably arranged so it
may face an almost same direction as a direction of alignment of a
liquid crystal molecule in a thick direction middle (mid-plane) of
a liquid crystal cell, which is aligned by voltage applied from
upper side and lower side. In aforesaid case, an alignment of the
liquid cell may be twisted type or non-twisted type.
The reflective semi-transmission type liquid crystal display of the
FIG. 9 is shown as an example of liquid crystal cells, and, in
addition to the example, a laminated optical film and an
elliptically polarizing plate of the present invention may be used
in various kinds of liquid crystal displays.
In addition, a transflective type polarizing plate may be obtained
by preparing the above-mentioned reflective layer as a
transflective type reflective layer, such as a half-mirror etc.
that reflects and transmits light. A transflective type polarizing
plate is usually prepared in the backside of a liquid crystal cell
and it may form a liquid crystal display unit of a type in which a
picture is displayed by an incident light reflected from a view
side (display side) when used in a comparatively well-lighted
atmosphere. And this unit displays a picture, in a comparatively
dark atmosphere, using embedded type light sources, such as a back
light built in backside of a transflective type polarizing plate.
That is, the transflective type polarizing plate is useful to
obtain of a liquid crystal display of the type that saves energy of
light sources, such as a back light, in a well-lighted atmosphere,
and can be used with a built-in light source if needed in a
comparatively dark atmosphere etc.
The polarizing plate with which a polarizing plate and a brightness
enhancement film are adhered together is usually used being
prepared in a backside of a liquid crystal cell. A brightness
enhancement film shows a characteristic that reflects linearly
polarized light with a predetermined polarization axis, or
circularly polarized light with a predetermined direction, and that
transmits other light, when natural light by back lights of a
liquid crystal display or by reflection from a back-side etc.,
comes in. The polarizing plate, which is obtained by laminating a
brightness enhancement film to a polarizing plate, thus does not
transmit light without the predetermined polarization state and
reflects it, while obtaining transmitted light with the
predetermined polarization state by accepting a light from light
sources, such as a backlight. This polarizing plate makes the light
reflected by the brightness enhancement film further reversed
through the reflective layer prepared in the backside and forces
the light re-enter into the brightness enhancement film, and
increases the quantity of the transmitted light through the
brightness enhancement film by transmitting a part or all of the
light as light with the predetermined polarization state. The
polarizing plate simultaneously supplies polarized light that is
difficult to be absorbed in a polarizer, and increases the quantity
of the light usable for a liquid crystal picture display etc., and
as a result luminosity may be improved. That is, in the case where
the light enters through a polarizer from backside of a liquid
crystal cell by the back light etc. without using a brightness
enhancement film, most of the light, with a polarization direction
different from the polarization axis of a polarizer, is absorbed by
the polarizer, and does not transmit through the polarizer. This
means that although influenced with the characteristics of the
polarizer used, about 50 percent of light is absorbed by the
polarizer, the quantity of the light usable for a liquid crystal
picture display etc. decreases so much, and a resulting picture
displayed becomes dark. A brightness enhancement film does not
enter the light with the polarizing direction absorbed by the
polarizer into the polarizer but reflects the light once by the
brightness enhancement film, and further makes the light reversed
through the reflective layer etc. prepared in the backside to
re-enter the light into the brightness enhancement film. By this
above-mentioned repeated operation, only when the polarization
direction of the light reflected and reversed between the both
becomes to have the polarization direction which may pass a
polarizer, the brightness enhancement film transmits the light to
supply it to the polarizer. As a result, the light from a backlight
may be efficiently used for the display of the picture of a liquid
crystal display to obtain a bright screen.
A diffusion plate may also be prepared between brightness
enhancement film and the above described reflective layer, etc. A
polarized light reflected by the brightness enhancement film goes
to the above described reflective layer etc., and the diffusion
plate installed diffuses passing light uniformly and changes the
light state into depolarization at the same time. That is, the
diffusion plate returns polarized light to natural light state.
Steps are repeated where light, in the unpolarized state, i.e.,
natural light state, reflects through reflective layer and the
like, and again goes into brightness enhancement film through
diffusion plate toward reflective layer and the like. Diffusion
plate that returns polarized light to the natural light state is
installed between brightness enhancement film and the above
described reflective layer, and the like, in this way, and thus a
uniform and bright screen may be provided while maintaining
brightness of display screen, and simultaneously controlling
non-uniformity of brightness of the display screen. By preparing
such diffusion plate, it is considered that number of repetition
times of reflection of a first incident light increases with
sufficient degree to provide uniform and bright display screen
conjointly with diffusion function of the diffusion plate.
The suitable films are used as the above-mentioned brightness
enhancement film. Namely, multilayer thin film of a dielectric
substance; a laminated film that has the characteristics of
transmitting a linearly polarized light with a predetermined
polarizing axis, and of reflecting other light, such as the
multilayer laminated film of the thin film having a different
refractive-index anisotropy (D-BEF and others manufactured by 3M
Co., Ltd.); an aligned film of cholesteric liquid-crystal polymer;
a film that has the characteristics of reflecting a circularly
polarized light with either left-handed or right-handed rotation
and transmitting other light, such as a film on which the aligned
cholesteric liquid crystal layer is supported (PCF350 manufactured
by Nitto Denko CORPORATION, Transmax manufactured by Merck Co.,
Ltd., and others); etc. may be mentioned.
Therefore, in the brightness enhancement film of a type that
transmits a linearly polarized light having the above-mentioned
predetermined polarization axis, by arranging the polarization axis
of the transmitted light and entering the light into a polarizing
plate as it is, the absorption loss by the polarizing plate is
controlled and the polarized light can be transmitted efficiently.
On the other hand, in the brightness enhancement film of a type
that transmits a circularly polarized light as a cholesteric
liquid-crystal layer, the light may be entered into a polarizer as
it is, but it is desirable to enter the light into a polarizer
after changing the circularly polarized light to a linearly
polarized light through a retardation plate, taking control an
absorption loss into consideration. In addition, a circularly
polarized light is convertible into a linearly polarized light
using a quarter wavelength plate as the retardation plate.
A retardation plate that works as a quarter wavelength plate in a
wide wavelength ranges, such as a visible-light band, is obtained
by a method in which a retardation layer working as a quarter
wavelength plate to a pale color light with a wavelength of 550 nm
is laminated with a retardation layer having other retardation
characteristics, such as a retardation layer working as a
half-wavelength plate. Therefore, the retardation plate located
between a polarizing plate and a brightness enhancement film may
consist of one or more retardation layers.
In addition, also in a cholesteric liquid-crystal layer, a layer
reflecting a circularly polarized light in a wide wavelength
ranges, such as a visible-light band, may be obtained by adopting a
configuration structure in which two or more layers with different
reflective wavelength are laminated together. Thus a transmitted
circularly polarized light in a wide wavelength range may be
obtained using this type of cholesteric liquid-crystal layer.
Moreover, the polarizing plate may consist of multi-layered film of
laminated layers of a polarizing plate and two of more of optical
layers as the above-mentioned separated type polarizing plate.
Therefore, a polarizing plate may be a reflection type elliptically
polarizing plate or a semi-transmission type elliptically
polarizing plate, etc. in which the above-mentioned reflection type
polarizing plate or a transflective type polarizing plate is
combined with above described retardation plate respectively.
Assembling of a liquid crystal display may be carried out according
to conventional methods. That is, a liquid crystal display is
generally manufactured by suitably assembling several parts such as
a liquid crystal cell, optical films and, if necessity, lighting
system, and by incorporating driving circuit. In the present
invention, except that an elliptically polarizing plate by the
present invention is used, there is especially no limitation to use
any conventional methods. Also any liquid crystal cell of arbitrary
type, such as TN type, and STN type, .pi. type may be used.
Suitable liquid crystal displays, such as liquid crystal display
with which the above-mentioned elliptically polarizing plate has
been located at one side or both sides of the liquid crystal cell,
and with which a backlight or a reflector is used for a lighting
system may be manufactured. In this case, the optical film by the
present invention may be installed in one side or both sides of the
liquid crystal cell. When installing the optical films in both
sides, they may be of the same type or of different type.
Furthermore, in assembling a liquid crystal display, suitable
parts, such as diffusion plate, anti-glare layer, antireflection
film, protective plate, prism array, lens array sheet, optical
diffusion plate, and backlight, may be installed in suitable
position in one layer or two or more layers.
Subsequently, organic electro luminescence equipment (organic EL
display) will be explained. Generally, in organic EL display, a
transparent electrode, an organic luminescence layer and a metal
electrode are laminated on a transparent substrate in an order
configuring an illuminant (organic electro luminescence
illuminant). Here, an organic luminescence layer is a laminated
material of various organic thin films, and much compositions with
various combination are known, for example, a laminated material of
hole injection layer comprising triphenylamine derivatives etc., a
luminescence layer comprising fluorescent organic solids, such as
anthracene; a laminated material of electronic injection layer
comprising such a luminescence layer and perylene derivatives,
etc.; laminated material of these hole injection layers,
luminescence layer, and electronic injection layer etc.
An organic EL display emits light based on a principle that
positive hole and electron are injected into an organic
luminescence layer by impressing voltage between a transparent
electrode and a metal electrode, the energy produced by
recombination of these positive holes and electrons excites
fluorescent substance, and subsequently light is emitted when
excited fluorescent substance returns to ground state. A mechanism
called recombination which takes place in a intermediate process is
the same as a mechanism in common diodes, and, as is expected,
there is a strong non-linear relationship between electric current
and luminescence strength accompanied by rectification nature to
applied voltage.
In an organic EL display, in order to take out luminescence in an
organic luminescence layer, at least one electrode must be
transparent. The transparent electrode usually formed with
transparent electric conductor, such as indium tin oxide (ITO), is
used as an anode. On the other hand, in order to make electronic
injection easier and to increase luminescence efficiency, it is
important that a substance with small work function is used for
cathode, and metal electrodes, such as Mg-Ag and Al-Li, are usually
used.
In organic EL display of such a configuration, an organic
luminescence layer is formed by a very thin film about 10 nm in
thickness. For this reason, light is transmitted nearly completely
through organic luminescence layer as through transparent
electrode. Consequently, since the light that enters, when light is
not emitted, as incident light from a surface of a transparent
substrate and is transmitted through a transparent electrode and an
organic luminescence layer and then is reflected by a metal
electrode, appears in front surface side of the transparent
substrate again, a display side of the organic EL display looks
like mirror if viewed from outside.
In an organic EL display containing an organic electro luminescence
illuminant equipped with a transparent electrode on a surface side
of an organic luminescence layer that emits light by impression of
voltage, and at the same time equipped with a metal electrode on a
back side of organic luminescence layer, a retardation plate may be
installed between these transparent electrodes and a polarizing
plate, while preparing the polarizing plate on the surface side of
the transparent electrode. Since the retardation plate and the
polarizing plate have function polarizing the light that has
entered as incident light from outside and has been reflected by
the metal electrode, they have an effect of making the mirror
surface of metal electrode not visible from outside by the
polarization action. If a retardation plate is configured with a
quarter wavelength plate and the angle between the two polarization
directions of the polarizing plate and the retardation plate is
adjusted to .pi./4, the mirror surface of the metal electrode may
be completely covered. This means that only linearly polarized
light component of the external light that enters as incident light
into this organic EL display is transmitted with the work of
polarizing plate. This linearly polarized light generally gives an
elliptically polarized light by the retardation plate, and
specially the retardation plate is a quarter wavelength plate, and
moreover when the angle between the two polarization directions of
the polarizing plate and the retardation plate is adjusted to
.pi./4, it gives a circularly polarized light.
This circularly polarized light is transmitted through the
transparent substrate, the transparent electrode and the organic
thin film, and is reflected by the metal electrode, and then is
transmitted through the organic thin film, the transparent
electrode and the transparent substrate again, and is turned into a
linearly polarized light again with the retardation plate. And
since this linearly polarized light lies at right angles to the
polarization direction of the polarizing plate, it cannot be
transmitted through the polarizing plate. As the result, mirror
surface of the metal electrode may be completely covered.
EXAMPLES
The present invention will, hereinafter, be described in detail in
reference to Examples; this invention is not limited to them at
all. Part represents part by weight in each Example.
In measurement of a refractive index and a retardation of each
optical film, principal refractive indexes nx, ny, and nz inside of
a film plane and in a thickness direction were measured for those
characteristics in .lambda.=590 nm, using an automatic
birefringence measuring apparatus (manufactured by Oji Scientific
Instruments, automatic birefringence meter KOBRA21 ADH).
In the optical film (2), an tilting angle that was mad by an
average optical axis of an optical material having tilted alignment
and a direction of normal line of the optical film (2) were
inclined -50 degrees to 50 degrees to right and left centering on
slow axis in the optical film (2), and thus a retardation was
measured with the measuring apparatus. An absolute value of an
angle showing a minimum retardation was adopted. Besides, in
measurement, a measured angle was set as 0 degree, when a normal
line to a film plane is in agreement with a direction of incidence
of a light from a light source of a measuring instrument.
Example 1
(Optical Film (1) having a Controlled Three Dimensional Refractive
Index)
Thermally shrinkable films comprising biaxial stretching polyester
film were attached on both sides of a transparent polycarbonate
film having a thickness of 70 micrometers via pressure sensitive
adhesive layers. Subsequently, obtained film was held in a
simultaneous biaxial stretching machine, and was stretched 1.1
times at 155 degrees C. An obtained stretched film had a thickness
72 micrometers, a front retardation: 140 nm and a thickness
direction retardation: 70 nm, and an Nz coefficient: 0.5.
(Optical Film (2) in which a Material Showing Optically Negative
Uniaxial Property is Tilting Aligned)
WVSA12B manufactured by FUJI PHOTO FILM CO., LTD. (thickness: 110
micrometers) was used. The film concerned was manufactured by
coating a discotic liquid crystal to a supporting medium, and had a
front retardation: 30 nm, a thickness direction retardation: 160
nm, and tilting angle of an average optical axis being tilting
aligned: 20 degrees.
(Optical Film (3) Showing Optically Positive Uniaxial Property)
A norbornene-based film having a thickness of 100 micrometers
(manufactured by JSR, Inc., product name Arton) was uniaxially
stretched 1.5 times at 170 degrees C. Obtained stretched film had a
thickness: 75 micrometers, a front retardation: 270 nm, and a
thickness direction retardation: 270 nm.
(Laminated Optical Film and Elliptically Polarizing Plate)
The optical film (1) and the optical film (2) were laminated via a
pressure sensitive adhesive layer (acrylic based pressure sensitive
adhesive: thickness 30 micrometers) to obtain a laminated optical
film (FIG. 1). Subsequently, the optical film (3) was laminated on
a side of the optical film (1) of the laminated optical film via a
pressure sensitive adhesive layer (acrylic based pressure sensitive
adhesive: thickness 30 micrometers) to obtain a laminated optical
film (FIG. 2). Furthermore, a polarizing plate (P: manufactured by
NITTO DENKO CORP., TEG1465DU) was laminated on a side of the
optical film (3) of the laminated optical film, via a pressure
sensitive adhesive layer (acrylic based pressure sensitive
adhesive: thickness 30 micrometers) to obtain an elliptically
polarizing plate (FIG. 5).
Example 2
(Optical Film (1) having a Controlled Three Dimensional Refractive
Index)
Thermal shrinkable films comprising biaxially stretched polyester
film were attached on both sides of a transparent polycarbonate
film having a thickness of 70 micrometers via pressure sensitive
adhesive layers. Subsequently, obtained film was held in a
simultaneous biaxial stretching machine, and was stretched 1.05
times at 165 degrees C. Obtained stretched film had a thickness: 75
micrometers, a front retardation: 140 nm, a thickness direction
retardation: 0 nm, and an Nz coefficient: 0.
(Laminated Optical Film and Elliptically Polarizing Plate)
Except for having used a stretched film manufactured above as an
optical film (1) in Example 1, a same method as in Example 1 was
repeated to obtain a laminated optical film and an elliptically
polarizing plate.
Example 3
The optical film (1), the optical film (2), the optical film (3),
and the polarizing plate (P) that were used in Example 1 were
laminated in an order of optical film (1)/optical film (2)/optical
film (3)/polarizing plate (P) via pressure sensitive adhesive
layers (acrylic based pressure sensitive adhesive: thickness 30
micrometers) to obtain an elliptically polarizing plate (FIG.
6).
Example 4
The optical film (1), the optical film (2), the optical film (3),
and the polarizing plate (P) that were used in Example 1 were
laminated in an order of optical film (1)/optical film (3)/optical
film (2)/polarizing plate (P), via pressure sensitive adhesive
layers (acrylic based pressure sensitive adhesive: thickness 30
micrometers) to obtain an elliptically polarizing plate (FIG.
7).
Comparative Example 1
(Retardation Film)
A transparent polycarbonate film having a thickness of 70
micrometers was uniaxially stretched 1.15 times at 155 degrees C.,
using a uniaxial stretching machine. Obtained stretched film had a
thickness: 60 micrometers, a front retardation: 140 nm, a thickness
direction retardation: 140 nm, and an Nz coefficient: 1.
(Laminated Optical Film and Elliptically Polarizing Plate)
Except for having used a retardation film (stretched film)
manufactured above instead of the optical film (1) in Example 1, a
same method as in Example 1 was repeated to obtain a laminated
optical film and an elliptically polarizing plate.
Referential Example 1
(Optical Film (3) Showing Optically Positive Uniaxial Property)
A norbornene-based film (manufactured by JSR, Inc., product name
Arton) having a thickness of 100 micrometers was uniaxially
stretched 1.3 times at 170 degrees C. Obtained stretched film had a
thickness: 80 micrometers, a front retardation: 140 nm, and a
thickness direction retardation: 140 nm.
This was named as optical film (3-2).
(Elliptically Polarizing Plate)
The optical film (3) showing optically positive uniaxial property
obtained in Example 1 was used as an optical film (3-1). As shown
in FIG. 8, the optical film (3-1) and the optical film (3-2)
concerned were laminated to a polarizing plate (P: manufactured by
NITTO DENKO CORP., TEG1465DU) via a pressure sensitive adhesive
layer (acrylic based pressure sensitive adhesive: thickness 30
micrometers) to obtain an elliptically polarizing plate.
(Evaluation)
The elliptically polarizing plate manufactured in Examples and
Comparative example was mounted as elliptically polarizing plates
(P1) on a side of a backlight of a reflective semi-transmission
type TFT-TN type liquid crystal display in FIG. 9. On the other
hand, the elliptically polarizing plate manufactured in Referential
Example 1 was mounted as an elliptically polarizing plate (P2) on a
viewing side. Both of the elliptically polarizing plates (P1) and
the elliptically polarizing plates (P2) were mounted so that a
polarizing plate side might be arranged in a lamination position
most separated from a liquid crystal cell (L) side.
Subsequently, Y value, x value, and y value in XYZ colorimetric
system in front and vertical and horizontal, and 0 to 70 degrees in
viewing angles were measured, using an EZcontrast160D made by ELDIM
SA. in a state where white picture and black picture were being
displayed on the above-mentioned liquid crystal displays.
An angle giving 10 of value of contrast or more at that time (Y
value (white picture)/Y value (black picture)) was defined as a
viewing angle. Table 1 shows the results.
Moreover, a chromaticity variation of chromaticity (x.sub.40,
y.sub.40) in a state of being vertically and horizontally tilted 40
degrees to a chromaticity (x.sub.0, y.sub.0) in front of a screen,
respectively, was measured and evaluated about white picture. A
chromaticity variation was calculated by a following equation.
Table 1 shows the results.
Chromaticity variation=√ {(x.sub.40 -x.sub.0).sup.2 +(y.sub.40
-y.sub.0).sup.2 }
TABLE 1 Comparative Example 1 Example 2 Example 3 Example 4 example
1 Chroma- Chroma- Chroma- Chroma- Chroma- Viewing ticity Viewing
ticity Viewing ticity Viewing ticity Viewing ticity angle variation
angle variation angle variation angle variation angle variation
(degree) (-) (degree) (-) (degree) (-) (degree) (-) (degree) (-)
Viewed in 25 0.30 28 0.28 20 0.32 17 0.33 13 0.35 inclined
direction (Upper direction) Viewed in 27 0.28 30 0.28 20 0.31 18
0.33 15 0.33 inclined direction (Lower direction) Viewed in 25 0.27
27 0.27 22 0.29 22 0.29 14 0.30 inclined direction (Left direction)
Viewed in 25 0.27 27 0.27 23 0.20 22 0.29 14 0.30 inclined
direction (Right direction)
* * * * *